Old-age deficits in the sense of smell as gauged by thresholds, magnitude matching, and odor identification

Twenty elderly subjects (70-90 years old) and 20 young control subjects (18-24 years old) underwent three kinds of olfactory testing: absolute thresholds to three odorants (d-limonene, iso-amyl butyrate, benzaldehyde), magnitude matching of these odorants to salt tastes, and odor identification of 30 common substances. For all three odorants elderly subjects' mean threshold significantly exceeded that of the young by about ninefold for d-limonene, about threefold for benzaldehyde, and about twofold for iso-amyl butyrate. These threshold differences predict approximate concentration differences necessary to arouse the same estimated odor strength above the threshold for the elderly and the young. Young subjects also scored better than the elderly in odor identification, even when subjects were given four alternatives from which to select the correct label. Unimpaired olfactory functioning is uncommon in the elderly; correlational tests show that as a group the young have better olfactory ability and show more interindividual uniformity.     

Sensory and semantic factors in recognition memory for odors and graphic stimuli: elderly versus young persons

In four experiments, young (18-26 years, M = 21) and elderly (over 65 years, M = 72) people were compared for recognition memory of (a) graphic stimuli (faces of presidents and vice presidents, engineering symbols, and free forms) and (b) everyday odors. On graphic stimuli, the elderly consistently matched the young, but on odors the performance of the elderly was worse. Their poorer olfactory performance was observed after only 26 s, but became truly marked after 1 hr or more. Somewhere between 1 hr and 2 weeks, their odor performance fell to chance, but their graphic performance remained well above chance. Although the young did forget both graphic and odor materials progressively, their performance always stayed above chance over a 6-month period. Experiments 1 and 2 revealed that the elderly are less sensitive to odors than the young (with thresholds about 10-fold higher), which may explain, in part, their poorer olfactory memory performance. Knowledge that the subjects brought to the tasks by way of familiarity with and ability to name odors and faces played a positive role in recognition memory. Because of this positive role, together with the negative role played by verbal distraction, we conclude that odor recognition memory depends, perhaps heavily, on semantic processing. Impaired semantic processing may result even when odors are simply rendered desaturated, or pastel because of the weakening of olfactory sensitivity with aging.     

Apolipoprotein epsilon4 is associated with more rapid decline in odor identification than in odor threshold or Dementia Rating Scale scores

Individuals with the apolipoprotein E epsilon4 genetic risk factor for Alzheimer's disease (AD) show deficits in olfactory function. The purpose of the present study was to examine longitudinally odor identification (odor ID), odor threshold, picture identification, and global cognitive status in allele positive (epsilon4+) and negative (epsilon4-) persons. Participants were initially given the San Diego Odor Identification test, an odor threshold test, and the Dementia Rating Scale (DRS). Participants were re-tested approximately four years later. The results indicate: (1) odor ID declined more rapidly in epsilon4+ than in epsilon4- normal elderly adults; (2) neither group exhibited a significant decline in odor threshold, picture identification or DRS scores. These results suggest that declines in odor identification occur before declines in other measures of dementia in persons at risk for AD because of their APOE allele genetic status.     

The nature and duration of adaptation following long-term odor exposure

Any individual living or working in an odorous environment can experience changes in odor perception, some of which are long lasting. Often, these individuals report a significant reduction in the perception of an odor following long-term exposure to that odor (adaptation). Yet, most experimental analyses of olfactory adaptation use brief odorant exposures which may not typify real-world experiences. Using a procedure combining long-term odor exposure in a naturalistic setting with psychophysical tests in the laboratory, we present evidence to show that reduced odor intensity following long-term exposure is accompanied by odorant-specific shifts in threshold. Subjects were exposed continuously to one of two odorants while in their home for a period of 2 weeks. Exposure produced an odorant-specific reduction in sensitivity and perceived intensity compared with preexposure baselines: Detection thresholds for the adapting odorant were elevated following exposure and perceived intensity ratings for weak concentrations were reduced. For most individuals, reduced sensitivity to the test odorant was still evident up to 2 weeks following the last exposure. The persistence of the change, as evidenced by the duration of recovery from adaptation, distinguishes this phenomenon from the adaptation seen following shorter exposures and highlights the need for the study of exposure durations that are more similar to real-world exposures.     

Variability of olfactory threshold and its role in assessment of aging

Olfactory thresholds of elderly persons (over 65 years) average one to two orders of magnitude higher than those of young adults (under 30 years). Past studies reveal enormous spreads (typically about three orders of magnitude) of individual thresholds within each age group and extensive overlap between the two groups—enough to question how typically decline in sensitivity characterizes the individual aged person. The present study shows that much of the observed overlap is misleading, because the brief threshold tests usually administered tend to exaggerate individual differences. A more representative assessment of an individual’s threshold (for 1-butanol) was achieved by averaging the thresholds from two to eight separate short tests, spread over 4 days. The spread of each group’s thresholds (12 young and 12 elderly subjects) narrowed strikingly as the number of tests averaged increased from one to four; further tests accomplished no additional narrowing of spread. Based on a single test, thresholds of young and elderly overlapped in the usual way; but based on four or more tests, thresholds of young and elderly overlapped little or not at all. The outcome (1) argues that decline in smell sensitivity seems to be, after all, a common feature of aging, and (2) sheds light on the sourcesof variability of sensory thresholds.     

Identification of odors of edible and nonedible stimuli as affected by age and gender

This study investigated cued odor identification performance with a set of 64 natural common odors (half of edible and half of nonedible stimuli) in three groups of participants: one group of 30 young adults (mean age 25.3 years, range 18-30, SD 3.1) and two groups of older adults-20 young-old (mean age 64.4 years, range 60-69, SD 2.8) and 21 old-old (mean age 74.6 years, range 70-79, SD 2.5). The results showed that 49 of the 64 odors were correctly identified by over 70% of the participants in all groups. The odor identification performance of the young-old adults did not differ from that of the young adults. However, the oldest group showed a significant loss of performance in the task. Women in the young-old group performed better than men, whereas no gender differences were found in the other two age groups. The data obtained in this study will be useful for further perceptual and memory studies conducted in the olfactory modality with young as well as with older participants.     

Time delays prior to movement alter the drawing kinematics of elderly adults

Position sense has been found to decay as a function of the time delay the limb remains in a static position prior to movement onset. Position sense has also been found to deteriorate as a function of aging, with increased reliance on vision by the elderly. This study investigated whether the pointing kinematics of elderly adults were differentially affected by delay compared to young adults, and whether visual information could compensate for the effects of delay. Young and elderly adults kept the limb in a static position for 1, 6, or 10 s prior to movement onset, both with and without vision of the limb, initial position, and the movement trajectory. Across groups, delay resulted in increased overall movement duration, decreased peak velocity including a shorter relative time to peak velocity, with decreased distance and duration of the primary submovement. Delay and lack of vision differentially decreased distance of the primary submovement for elderly adults. Vision was able to compensate to some degree for the effects of delay across age groups. The findings provide evidence that decays in position sense as a function of time create difficulties in incorporating the initial limb position in motor planning process in elderly adults.     

On the consistency of intramodal intensity matching in olfaction

Magnitude matchings of odor intensity were obtained for three chemical compounds (hydrogen sulfide, pyridine, and dimethyl disulfide) in four experiments. An equal-sensation function in the form of a power function described the data well. This equation can be written neglecting the multiplicative constant, Ф_i = Ф_k ^b _ik, where i and k represent two different odorants. The exponent b_ik, where the first index stands for matching continuum and the second index for reference continuum, was fairly well predicted according to the formulae, (ie, 264, 2) where i, j, and k are three different odorants. The results validate the equal-sensation function and indicate implicitly that intensity matchings between different intramodal continua are approximately transitive and symmetric with respect to odor.     

Odor quality: Discrimination versus free and cued identification

Eighty-two adults, ranging in age from young to elderly, performed odor-quality discrimination and both free and cued identification on six odorants presented at two intensity levels. The odorants simulated the real-world substances banana, licorice, cherry/almond, wintergreen, clove, and lemon. Performance on all three tasks declined with age, but improved with stimulus intensity. Performance at discrimination benefited from the mere availability of the six names during testing. Performance in cued identification far exceeded that in free identification and, for young and middle-aged adults, fell close to that for discrimination. For elderly adults, however, performance in cued identification fell substantially below that in discrimination. Although not entirely free of cognitive influences, discrimination seems to offer particularly clear resolution of alterations in olfactory functioning.     

Age and culture modulate object processing and object—scene binding in the ventral visual area

Behavioral differences in the visual processing of objects and backgrounds as a function of cultural group are well documented. Recent neuroimaging evidence also points to cultural differences in neural activation patterns. Compared with East Asians, Westerners’ visual processing is more object focused, and they activate neural structures that reflect this bias for objects. In a recent adaptation study, East Asian older adults showed an absence of an object-processing area but normal adaptation for background areas. In the present study, 75 young and old adults (half East Asian and half Western) were tested in an fMR-adaptation study to examine differences in object and background processing as well as object—background binding. We found equivalent background processing in the parahippocampal gyrus in all four groups, diminished binding processes in the hippocampus in elderly East Asians and Westerners, and diminished object processing in elderly versus young adults in the lateral occipital complex. Moreover, elderly East Asians showed significantly less adaptation response in the object areas than did elderly Westerners. These findings demonstrate the malleability of perceptual processes as a result of differences in cohort-specific experiences or in cultural exposure over time.     

Lingual vibrotactile threshold shift during magnitude-estimation scaling: effects on magnitude-estimation responses and scaling behavior across age

The purpose of this study was to investigate the effects of age on tactile threshold shifts occurring during magnitude-estimation scaling of vibratory stimuli presented to the dorsal surface of the tongue. Relationships of the lingual vibrotactile threshold shifts to suprathreshold stimulus intensity, magnitude-estimation responses, and over-all scaling behavior were explored. Three groups differing in mean age participated in this study (Group 1 8.05 yr., Group 2 19.46 yr., and Group 3 56.2 yr.). Each subject performed two magnitude-estimation tasks. In one task, threshold of sensitivity was measured after every suprathreshold numerical response to the subject. If a threshold shift was recorded, threshold was allowed to return to the pretest baseline level continuing to the next suprathreshold stimulus presentation. The results showed that threshold shift during magnitude-estimation scaling took place for all three age groups and that the shift was related to the intensity of the suprathreshold vibratory stimulus being applied to the tongue. They also showed that Group 2 (young adults) performed magnitude-estimation scaling differently when threshold shift was controlled than when it was not. The other two groups of subjects were not similarly affected.     

Diminished motor skill development in elderly: Indications for limited motor chunk use

The present study examined whether elderly use motor chunks after practicing discrete keying sequences, just like young adults, or whether they perhaps learn these movement patterns in a different way. To that end, elderly (75-88) and young adults (18-28) practiced as part of the discrete sequence production (DSP) task two fixed series of three and six key presses. The results demonstrate that elderly did improve with practice but this improvement was largely sequence-unspecific. Detailed analyses showed that, in contrast to young adults, most elderly did not use motor chunks, had little explicit sequence knowledge, and remained highly dependent on external stimuli. Still, elderly did show sequence-specific learning with a 6-key sequence that can be explained by an associative learning mechanism.     

Dissociations in perceptual learning revealed by adult age differences in adaptation to time-compressed speech

When presented with several time-compressed sentences, young adults' performance improves with practice. Such adaptation has not been studied in older adults. To study age-related changes in perceptual learning, the authors tested young and older adults' ability to adapt to degraded speech. First, the authors showed that older adults, when equated for starting accuracy with young adults, adapted at a rate and magnitude comparable to young adults. However, unlike young adults, older adults failed to transfer this learning to a different speech rate and did not show additional benefit when practice exceeded 20 sentences. Listeners did not adapt to speech degraded by noise, indicating that adaptation to time-compressed speech was not attributable to task familiarity. Finally, both young and older adults adapted to spectrally shifted noise-vocoded speech. The authors conclude that initial perceptual learning is comparable in young and older adults but maintenance and transfer of this learning decline with age.     

Memory for internally generated words in Alzheimer-type dementia: breakdown in encoding and semantic memory

The "generation effect" is a phenomenon in which words that are generated by the subject are remembered better than words which are read. The present experiments examined this effect in patients with mild-to-moderate dementia of the Alzheimer type (DAT), healthy elderly adults, and young adults under a variety of different encoding and retrieval conditions. Experiment 1 employed an intentional learning task with multiple study/test trials using the same list of words. While both the young and elderly adults exhibited higher recall for internally generated words than read words, the DAT patients failed to demonstrate the effect even after repeated exposures to the same stimulus list. Experiment 2 replicated this same pattern of results using an incidental learning paradigm with both recall and recognition tests. Various explanations as to why the DAT patients failed to show the generation effect were discussed with particular emphasis placed on the role of semantic memory and encoding failure.     

Conjunction errors in recognition memory: modality-free errors for older adults but not for young adults

A dual-process theory of memory was applied to processes in normal aging, with a focus on recognition errors in the feature-conjunction paradigm (i.e., false recognition of blackbird after studying parent words blackmail and/or jailbird). Study repetition was manipulated so that some parent words occurred once and others occurred three times. Age-related differences on hit scores occurred for two experiments. The results for feature and conjunction conditions showed repetition effects but no age-related differences when participants were uninformed of the lures (Experiment 1). However, age-related differences emerged when the retrieval of modality source information created a way to evade conjunction errors (Experiment 2). In the second experiment, study repetition decreased errors for the young adults but increased errors for the older adults, and young adults were better able than older adults to avoid conjunction errors when the parent words had been repeated. For older adults, the conjunction errors were modality-free. The results provide additional evidence that older adults experience difficulty in recollecting aspects of a study experience, and the results from groups of young adults required to respond quickly on the tests provide converging evidence for this conclusion.     

Aging and intuitive physics

The present study was aimed at comparing the judgment capacities manifested by young adults, middle-aged adults, and elderly people in an everyday life setting implying the consideration of direct as well as inverse relationships between the cues and the criterion. The chosen situation was borrowed from elementary physics and concerned the relationships between mass, volume and density. In forming their estimations of mass, all elderly people were able to use volume and density information. In addition, most of them were able to combine these pieces of information in a correct, multiplicative way. In forming their estimations of volume, all elderly people were able to use mass and density information but a majority of them used the density information in a direct way. By contrast, most young and middle-aged adults correctly used the density information in an inverse way. The findings strengthen and extend the case made by Chasseigne et al. [Acta Psychologica 97 (1997) 235] as regards the trouble elderly people face in using inverse relationships in a judgment situation. The difficulty elderly people face is not confined to learning settings. It may also be observed in ecological, non-learning environments, where the relationships considered do not entirely depend on the experimenter's choice.     

The effects of the age of eyewitnesses on the accuracy and suggestibility of their testimony

Previous studies have compared the performance of young adult eyewitnesses with that of children or elderly eyewitnesses, but few studies have allowed direct comparison of the performance of all three age groups. The accuracy and suggestibility of accounts of a video recording of a kidnapping were investigated using an experimental eyewitness paradigm. Subjects were drawn from three age groups: children (aged 7–9 years); young adults (aged 16–18 years) and elderly subjects (aged 60–85 years). Subjects' accuracy in answering non-misleading questions and their susceptibility to misleading information was measured. Both the elderly and child subjects gave fewer correct answers and more incorrect answers to non-misleading questions than did young adults. The elderly subjects gave fewer correct responses but also fewer incorrect responses to non-misleading questions than did child subjects. Children were more suggestible than either elderly or young adults. No significant difference was found in the suggestibility of elderly and young adults. Contrary to the trace strength hypothesis no relationship was found between accuracy of recall and suggestibility. © 1997 John Wiley & Sons, Ltd.     

When more is less: failure to compress discourse with re-telling in normal ageing

When young adults tell the same story repeatedly, their narratives become progressively more concise. Although impaired discourse production has been reliably demonstrated in the elderly, changes in narrative production with repetition have not been investigated in this cohort. Thirty young (aged 18-49 years, M=28.77, SD=9.73) and thirty elderly (aged 65+ years, M=73.57, SD=6.80) adults completed a discourse production task involving narrative construction using an eight-frame cartoon. Narratives were repeated 4 consecutive times. Variables analysed were narrative duration, word count and fluency (words/sec). For all variables the compression index for the elderly group was significantly lower than that for young participants. Further, compared to their younger counterparts, elderly adults were less able to improve the cohesion of their narratives with repetition. These findings suggest that the elderly have a reduced capacity to generate and refine discourse representations.     

Attentional modulation of desensitization to odor

Subjective and behavioral responsiveness to odor diminishes during prolonged exposure. The precise mechanisms underlying olfactory desensitization are not fully understood, but previous studies indicate that the phenomenon may be modulated by central-cognitive processes. The present study investigated the effect of attention on perceived intensity during exposure to a pleasant odor. A within-subjects design was utilized with 19 participants attending 2 sessions. During each session, participants continuously rated their perceived intensity of a 10-minute exposure to a pleasant fragrance administered using an olfactometer. An auditory oddball task was implemented to manipulate the focus of attention in each session. Participants were instructed to either direct their attention toward the sounds, but still to rate odor, or to focus entirely on rating the odor. Analysis revealed three 50-second time windows with significantly lower mean intensity ratings during the distraction condition. Curve fitting of the data disclosed a linear function of desensitization in the focused attention condition compared with an exponential decay function during distraction condition, indicating an increased rate of initial desensitization when attention is distracted away from the odor. In the focused-attention condition, perceived intensity demonstrated a regular pattern of odor sensitivity occurring at approximately 1?2 minutes intervals following initial desensitization. Spectral analysis of low-frequency oscillations confirmed the presence of augmented spectral power in this frequency range during focused relative to distracted conditions. The findings demonstrate for the first time modulation of odor desensitization specifically by attentional factors, exemplifying the relevance of top-down control for ongoing perception of odor.     

Effect of blank samples on absolute odor threshold determinations’

Absolute odor thresholds for methyl isobutyl ketone were estimated under five conditions: odor sample-to-air blank ratios of 1:2, 1:1, 2:1, 4:1, and 9:1. Each of the five ratios was presented in two replicated balanced Latin square sequences to five adult human Ss. The results showed that significantly lower estimates of the threshold were obtained when the ratio of odor samples to air blanks was 1:1. These results are discussed in terms of possible adaptation effects, maintenance of an internal frame of reference as a basis for decisions, and response matching to pay-off expectancy.